British light heavyweight Joshua Buatsi secured a victory yet unimpressive debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close 10-round contest at the Manchester venue.
But Parker had his moments, connecting with powerful clean blows in a fight where the techniques failed to mesh, with frequent clinching marring the action.
Two judges scored it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi stated in the ring as he was greeted with boos from the crowd.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in February - to secure a 20th career victory.
Some ringside observers felt the challenger, 31, should have been awarded the win but the Derbyshire fighter experienced the second defeat of his 28-match career.
The Champion Secures Victory in Uneventful Match
His career development has slowed in recent years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of British boxing, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under recent support.
He started carefully, with neither fighter willing to overcommit in a calculated initial rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in 2022 after breaking his hand in the contest, was making just his second bout at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who operated with a protective stance to narrowly win the cleaner stanzas.
The crowd's patience decreased because of regular grabbing, with the challenger falling to the floor several times during grappling.
The underdog closed well, but many rounds were challenging to assess. Although, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Hatton Memorial Inspires All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a excellent all-Manchester fight to secure the European light-heavyweight title.
The venue fell silent for a extremely emotional homage prior to the bout as 10 bells rang in memory of the city's native Hatton, who passed away at age 46 in September.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime faded, the quiet transitioned to a shout of "there's just one Hatton".
The action within the ring matched the sentiment. Arthur was floored by a left hook squarely on the chin in the early round, rising shakily to his footing on the count of eight.
But the red-colored equipment of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was marked up early, significant bruising developing under his face as the duo exchanged powerful shots.
The challenger, 27, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the intensity rarely dropped over 12 rounds.
The victor barely secured the verdict with scoring tallies of even score, 115-113 and 115-112, but each competitor were determined and courageous, all the qualities their hero Hatton represented.
